This application claims priority pursuant to Title 35, United States Code, Section 119(a)-(d) or (f), or 365(b) to the German Application Number 100 43 038.4 filed Sep. 1, 2000, by the same inventor, where the above named application is hereby incorporated herein by reference in its entirety including incorporated material.
The field of the invention is the testing of dispersion of particles and pigments in liquid and solid matrices.
The purpose of coatings is to protect and enhance the appearance of surfaces. Therefore, numerous methods have been developed for testing the properties of coatings. In the optical field, these include gloss and haze measurements, color measurements, determination of the contrast ratio or the determination of scattering coefficients. In the case of TiO2 pigments, these methods provide an indirect statement concerning the quality of distribution of these pigments in the polymer matrix. The finer the pigment particles are, and the more uniformly they are distributed in this matrix, the better will be the hiding power or the contrast ratio, the higher the gloss value, the lower the haze value and the greater the brightness. Electron micrographs of microsections of paint films provide a direct insight into the state of dispersion of the pigment in the coating. In practice, measurements are sometimes obtained for which there is no simple explanation. For instance, when used in a familiar formulation, a time-proven TiO2 pigment may produce a weaker contrast ratio in one production run that it did in a previous run, although the brightness and gloss values remain unchanged. The fault could lie in the formulation, the preparation of the coating, the dispersion process or the test method. Questions of this kind also arise when developing formulations. Does the pigment tend towards flocculation in one binder and towards finer distribution in another? What is the effect on the particle size distribution if the dispersing agent concentration is increased or reduced? The prior art is deficient in that It would take too much time and expense to answer these questions with the help of electron micrographs. Prior art methods of measuring pigment distribution by measuring transmission of light through the pigment matrix mix noted in U.S. Pat. Nos. 6,236,460 and 6,040,913 are deficient in that transparent substrates must be used and uniform thicknesses of thin material is necessary. The present invention is a method that permits the quick and simple observation of changes in the distribution of the pigment in the polymer matrix.
It is an object of the invention to provide a method of simply measuring the quality of dispersion or distribution value of pigment particles in a matrix. It is an object of the invention to provide a method of comparing one pigment dispersion sample with another. It is an object of the invention to provide a method of estimating pigment floculation. It is an object of the invention to provide a method of testing different matrices with the same pigment mix.
The present invention is a system, apparatus and method to measure the reflectivity of a sample of pigment dispersed in a solid or liquid matrix in at least two wavelength bands, and to determine the quality of the dispersion by calculating a function of the measured reflectivities. The most preferred embodiment of the invention is to measure the reflectivity F1 and F2 integrated over two broad bands of wavelengths xcex1xe2x88x92xcexm and xcexnxe2x88x92xcex2, and to derive a quality factor S proportional to the quotient F1/F2.